In recent years, a ventilator or an air conditioning system of an air conditioner is required to perform control so as to keep a predetermined airflow value even when static pressure varies due to clogging of a filter or a state of a vent provided at an air outlet, in order to optimize a state of a room or the air conditioning system.
As a technique for keeping the predetermined airflow value, for example, Patent Document 1 is known. According to the conventional art described in Patent Document 1, a relationship between a motor applied voltage and a motor speed is represented by equation (1).N=1.027×Kt×V/(Kp×R×Q×D2+1.027×Kt×Ke)  Equation (1)
Here, if a static pressure coefficient is Kp, a diameter of an impeller is D, a torque constant is Kt, a total resistance of an armature circuit is R, and an induced voltage constant is Ke, prescribed motor speed N is calculated from instruction airflow Q and applied voltage V to control applied voltage V so that an operating motor speed and the prescribed motor speed are equal.
In the conventional art described in Patent Document 1, in a process of deriving equation (1), motor current I is found from applied voltage V to the motor, and total resistance R of the armature circuit and induced voltage E, based on a relationship of equation (2).V=E+I×R  Equation (2)
In other words, instead of controlling motor current I, applied voltage V to the motor is controlled. However, there is a problem in that since total resistance R of the armature circuit varies due to heat generation of the motor and atmosphere temperature, motor current I cannot be accurately controlled due to the influence of total resistance R of the armature circuit even when applied voltage V to the motor is controlled, an error of the airflow occurs by the heat generation of the motor and the atmosphere temperature.
The present invention is made to solve the above conventional problem, and an object thereof is to provide a motor control device capable of maintaining a predetermined airflow value precisely by detecting a current of a motor against change factors such as temperature change, and its control method, and a motor device.
[Patent Document 1] Unexamined Japanese Patent Publication No. 6-153579